1. This document discusses thermodynamics concepts related to heat engines and refrigerators. It provides example calculations for efficiency of different heat engines like Stirling engines and Carnot engines. 2. Multiple choice questions are provided related to efficiency, heat transfer, temperature of hot/cold reservoirs in Carnot engines and refrigerators operating on Carnot cycle. 3. Formulas for efficiency of different heat engines and refrigerators are given along with sample calculations.

1. HEAT ENGINES AND REFRIGERATORS
THERMODYNAMICS
Department of Physics, Faculty of Science
Jazan University, KSA
Part-7
222 PHYS
MC questions

2. Lecture 13, p 2
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 
  
   
 
   
 
 

l
2
1
2
1
( )ln
( n 2 0.69)
3
( ) ln
2
100(0.69)
16.9%
150 373(0.69)
h c
by
h
h c h
V
T T
W V
Q V
T T T
V
Let’s put in some numbers:
V2 = 2V1
n = 3/2 (monatomic gas)
T2=Th = 373K (boiling water)
T1=Tc = 273K (ice water)
For comparison:
ηcarnot = 1 – 273/373 = 26.8%
1: find the efficiency of Stirling engine with the following parameters

3. 2: In a Carnot engine 800 J of heat is absorbed from a source at 400 K and 640 J of
heat is rejected to the sink. The temperature of the sink
is a) 320 K
b) 100 K
c) 273 K
d) 250 K
e) 200 K
3: A refrigerator operates in a cyclic and reversible manner (Carnot cycle).The
temperature inside the refrigerator is 0°C and the room temperature is 27°C. The
absorbed heat from the interior of the refrigerator Q1 = 334.72x103 J . If the
coefficient of performance of the refrigerator, COP= Q1/W .the magnitude of heat Q2
rejected in the room is:
a) 455.8J
b) 310.6 J
c) 367.8J
d) 340 J
e) None
c c
h h
Q T
Q T

2 1
2 1
ch
h c
QQ Q Q
T T T T
  

4. 5: The efficiency of a Carnot engine is 35.0%. What is the temperature of the cold
reservoir if the temperature of the hot reservoir is 500 K?
A) 175 K
B) 325 K
C) 269 K
D) 231 K

5. 6: The maximum efficiency of a heat engine that operates between temperatures
of 1000 K in the firing chamber and 600 K in the exhaust chamber is most
nearly
(A) 33% (B) 40% (C) 60% (D) 67% (E) 100%
7: The theoretical (Carnot) efficiency of a heat engine operating between 600C
and 100C is
A) 16.7 % B) 20.0 % C) 42.7 % D) 57.3 % E) 83.3 %
8: A heat engine takes in 200 J of thermal energy and performs 50 J of work in each
cycle. What is its efficiency?
A) 500 % B) 400 % C) 25 % D) 20 % E) 12 %

6. 9: A monoatomic ideal gas is used as the working substance for the Carnot
cycle shown in the figure. Processes A→B and C → D are isothermal,
while B → C and D → A are adiabatic. During process A
→ B, there are 400 J of work done by the gas on the
surroundings. How much heat is expelled
by the gas during process C → D?
A) 1600 J
B) 800 J
C) 400 J
D) 200 J
E) 100 J